Valve spring retainer for an internal combustion engine and a method of manufacturing the same

ABSTRACT

Oxide film formed on a spring-retaining flange by heat treatment gets unlikely to peel off, thereby improving wear resistance of a contact surface of the spring-retaining flange with a valve spring. The oxide film  15  of the part of the spring-retaining flange  3  with the valve spring  7  is at least partially removed to make thickness of the oxide film to 0.00 to 0.02 μm.

TECHNICAL FIELD

The present invention relates to a valve spring retainer used in a valvetrain of an internal combustion engine, and particularly to a valvespring retainer produced from metal sheet and a method of manufacturingit.

BACKGROUND OF THE INVENTION

The valve spring retainer made of metal sheet is lightened to reduceinertial mass of the valve train thereby improving the performance ofthe internal combustion engine in Patent Literatures 1-3.

PRIOR ART Patent Literatures

-   Patent Literature 1: JP55-17976A-   Patent Literature 2: JP62-185807A-   Patent Literature 3: JP2002-303107A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In the valve spring retainer made of metal sheet, a steel sheet ismolded by a press and an original of the valve spring retainer isformed. In order that wear resistance is improved, its surface ishardened The original is generally treated with heat such ascarburizing, quenching and tempering.

By heat treatment, a carburized layer is formed on the surface of thevalve spring retainer. At the same time, carburizing is carried out inan ordinary carburizing furnace other than a vacuum carburizing furnace,so that an oxide film is formed on the surface of the carburized layer.The oxide film provides hardness, so that a spring-retaining flange inthe valve spring retainer pressed by the upper end of the valve springis improved in wear resistance.

However, the spring-retaining flange is always in contact with the endface of the valve spring during running of the engine. When the valvespring is compressed, bending stress is exerted to the spring-retainingflange, which is flexed. The spring-retaining flange relatively slideson the valve spring. The oxide film formed on the part of thevalve-retaining flange pressed by the upper end of the valve springpeels off. By grinding effect of the peeled oxide, the contact surfacebetween the spring-retaining flange and the valve spring can be worn.The thicker the oxide film is, the more likely the problem occurs.

Particularly, the valve spring retainer made of metal sheet is thin, sothat it is necessary to prevent wear of the spring-retaining flange asmuch as possible.

In view of the disadvantages, it is an object of the invention toprovide a valve spring retainer in which oxide film formed on aspring-retaining flange by heat treatment is unlikely to peel offthereby improving wear resistance of a contact surface between thespring retaining flange and a valve spring, and a method ofmanufacturing it.

Means for Solving the Problems

According to the present invention, the foregoing problems are solved

(1) In a valve spring retainer made of metal sheet in an internalcombustion engine, comprising a frusto-conical part having taper hole atit center and a spring-retaining flange pressed by the upper end of avalve spring, the valve spring retainer being treated with heat bycarburizing, quenching and tempering, oxide film is formed by the heaton the surface at the spring-retaining flange pressed by the upper endof the valve spring and is at least partially removed so that the oxidefilm gets 0.00-0.02 μm.

The oxide film formed on the part at the spring-retaining flange pressedby the upper end of the valve spring is 0.00-0.02 μm thick, and getsmore difficult to peel off by sliding with the valve spring.

(2) In the item (1), a center line average on the surface of the part atthe spring-retaining flange pressed by the upper end of the valve springis not more than 1.20 μm.

Thus, by synergistic effect of the thickness 0.00-0.02 μm of the oxidefilm of the part at the spring-retaining flange pressed by the upper endof the valve spring with the center line average of not more than 1.20μm, the oxide film by sliding with the valve spring gets more difficultto peel off.

(3) In the item (2) or (3), the lower surface of the spring-retainingflange pressed by the upper end of the valve spring is tilted upward andoutward away from the valve spring.

Thus, a contact portion of the spring-retaining flange with the valvespring gets nearer to the center of the spring-retaining flange, so thatbending moment acting to the spring-retaining flange becomes smallerthan a contact portion away from the center and it gets more difficultto flex. Relative sliding with the valve spring involved flexing of thespring-retaining flange is restrained, and the oxide film formed on thecontact surface at the spring retaining flange with the valve springgets more unlikely to peel off.

The spring-retaining flange gets more unlikely to flex, so that fatiguestrength is improved.

(4) In any one of the items (1)-(3), the outer surface of a cornerbetween the frusto-conical part and the spring-retaining flange isformed as an arc with a radius of curvature larger than the thickness ofthe frusto-conical part, and the inner surface of the corner facing theouter surface is formed as an arc with a radius of curvature smallerthan the radius of curvature of the outer surface of the corner, so thatthe thickness of the corner is lager than the thickness of thefrusto-conical aprt.

The corner between the frusto-conical part and the spring-retainingflange is strengthened thereby improving bending rigidity, so that thespring-retaining flange gets more unlikely to flex. As well as theforegoing, peeling-off of the oxide film involved by flexing of thespring-retaining flange is prevented, so that stress does not gather tothe corner between the frusto-conical part and the spring-retainingflange, so that fatigue strength is improved.

(5) In a method of manufacturing the valve spring retainer for aninternal combustion engine of anyone of the items (1) to (4), the methodcomprises the deep-drawing step for drawing a circular metal sheet tomold an original of the valve spring retainer in which thespring-retaining flange is formed on the outer circumferential surfaceof the frusto-conical part with the taper hole; the heating step forheating the original by carburizing, quenching and tempering; and theoxide-film removing step for removing the oxide film so that itsthickness is 0.00-0.02 μm.

Thus, the metal sheet valve spring retainer in which the oxide film isformed at the contact surface of the spring-retaining flange with thevalve spring is 0.00-0.02 μm thick.

(6) In the item (5), the oxide film removing step includes grinding.

By the grinding, the oxide film formed on the contact surface at thespring-retaining flange with the valve spring can readily be removed tobecome predetermined thickness.

(7) In the item (6), by barrel finishing, center line average Ra of thepart at the spring-retaining flange pressed by the upper end of thevalve spring is not more than 1.20 μm.

By the barrel finishing to a number of valve spring retainers, the oxidefilm formed on the whole surface including the part at thespring-retaining flange pressed by the upper end of the valve spring canground to predetermined thickness, thereby improving productivity.

By determining grain size of grinding material, center line average Raof the part at the spring-retaining flange pressed by the upper end ofthe valve spring can be not more than 1.20 μm.

Advantages of the Invention

According to the present invention, the oxide film formed on thespring-retaining flange by heating gets more unlikely to peel off,thereby improving wear resistance of the contact surface of thespring-retaining flange with the valve spring.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of a valve springretainer according to the present invention.

FIG. 2 is a central vertical sectional front view of a valve train withthe valve spring retainer.

FIG. 3 is an enlarged sectional view of the valve spring retainer.

FIG. 4 is an enlarged sectional view of a surface layer.

FIG. 5 is an enlarged sectional view of the lower surface of aspring-retaining flange.

FIG. 6 is an enlarged sectional view of the lower surface of thespring-retaining flange after removing oxide film.

FIG. 7 is a graph showing the results of a wear test of thespring-retaining flange.

FIG. 8 is a diagram showing the steps of a method of manufacturing thevalve spring retainer according to the present invention.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described with respect tothe drawings.

FIG. 1 is a perspective view of one embodiment of a valve springretainer according to the present invention, and FIG. 2 is a centralvertical sectional view of a valve train in which the valve springretainer is mounted.

The valve spring retainer 1 is molded from low carbon steel sheet havingthickness of 1.2-1.6 mm mainly by deep drawing, and comprises aninverted frusto-conical part 2 and an outward spring-retaining flange 3at the upper end thereof.

Inward beads 5 a, 5 a of a pair of cotters 5,5 held in a taper hole 4 ofthe frusto-conical part 2 engage in annular groove 6 a to allow thevalve spring retainer 1 to be coupled to a poppet valve 6.

The upper end of a valve spring 7 the lower end of which is supported ona cylinder head (not shown) is in contact with the lower surface 3 aclose to the outer circumference of the spring-retaining flange 3, sothat the poppet valve 6 is forced upward.

An annular guide 8 is formed in the middle of the valve-retaining flange3, and the upper end of the valve spring 7 is in contact with thehorizontal lower surface close to the circumference.

The guide 8 prevents the upper end of the valve spring 7 from movingradially and provides large section modulus to increase bending rigidityof the spring-retaining flange 3. The guide 8 may preferably be 1.5-2.5mm long.

As shown in FIG. 3, the thickness T1 of a corner 9 between thefrusto-conical part 2 and the spring-retaining flange 3 is larger thanthe thickness T2 of the frusto-conical part 2. At the corner 9 betweenthe frusto-conical part 2 and the spring-retaining flange 3, an outersurface 10 is an arc with a radius of curvature which is larger than thethickness of the frusto-conical portion 2. An inner surface 11 whichfaces the outer surface 10 is an arc with a radius of curvature which islarger than the radius of curvature of the inner surface 10, so that thethickness of the corner 9 is larger than the thickness of thefrusto-conical portion 2.

The outer surface 10 of the corner 9 between the frusto-conical portion2 and the spring-retaining flange 3 is the arc with the radius ofcurvature larger than the thickness of the frusto-conical portion 2, andthe thickness T1 of the corner is larger than the thickness T2 of thefrusto-conical portion 2, so that the corner 9 is strengthened withincreased bending rigidity. Thus, stress is prevented from gathering tothe part, so that fatigue strength of the corner 9 is improved.

The spring-retaining flange 3 becomes unlikely to be bent, therebypreventing the spring-retaining flange 3 from sliding on the valvespring 7.

The lower surface of the spring-retaining flange 3 which contacts theupper end of the valve spring 7 is tilted upward and outward away fromthe upper end of the valve spring 7, so that the upper innercircumference of the valve spring 7 contacts the inner part of the outerlower surface 3 a of the spring-retaining flange 3. An angle of tiltwith respect to the lower surface 3 a may be less than 1.0 degree suchthat the inner circumference of the upper end of the valve spring 7 doesnot strongly contact the inner part of the outer lower surface 3 a.

If the valve spring retainer 1 is molded from relatively thick platehaving high bending rigidity or if the spring-retaining flange 3 issmall in diameter in the valve spring retainer 3, the outer lowersurface 3 may be horizontal.

By tilting the outer lower surface 3 a of the spring-retaining flange 3,the outer lower surface 3 a contacts the valve spring 7 at an innerpoint of the outer lower surface 3 a thereby reducing bending momentwhich exerts the spring-retaining flange 3. The inner point is notlikely to become flexing, thereby preventing the spring-retaining flange3 from sliding on the valve spring 7 and improving fatigue strength ofthe valve-retaining flange 3.

In the valve spring retainer 1 after press molding, in order to improvewear resistance of the surface and strength of each part, heat treatmentsuch as carburizing in a gas carburizing furnace, quenching andtempering is applied.

FIG. 4 is an enlarged sectional view of surface layers of the valvespring retainer 1 after the heat treatment. An about −0.1-0.5 mm-thickcarburized layer 13 which is formed on the whole surface of a matrix 12,and an about 0.2 μm-thick oxide film 14 is formed on the carburizedlayer 13 with the heat treatment.

In the valve spring retainer 1 according to the present invention, inFIG. 5, the oxide film 14 formed on the whole surface including theouter lower surface 3 a which is pressed by the upper end of the valvespring 7 is partially removed by mechanical means such as grinding sothat the oxide film becomes thinner to the thickness of 0.00-0.02 μm.

With or after partially removing of the oxide film 14, at least theouter lower surface 3 a pressed by the upper end of the valve spring 7at the spring-retaining flange 3 is finished to have surface roughnessor center-line average under JIS of more than 1.20 μm. Owing to theoxide film 14 having thickness of not more than 0.02 μm formed on theouter lower surface pressed by the upper end of the valve spring 7, theoxide film 14 on the lower surface of the spring-retaining flange 3 isprevented from peeling off or is unlikely to peel off even if the upperend of the valve spring 7 slides on the lower surface of thevalve-retaining flange 3 during running of an engine.

Because of synergistic effect of the 0.00-0.02 μm thickness of the oxidefilm 14 on the outer lower surface 3 a of the spring-retaining flange 3with the not-more-than 1.20 μm center line average Ra on the outer lowersurface 3 a the oxide film 14 is more unlikely to peel off duringsliding on the valve spring 7.

Why the center-line average Ra on the outer lower surface 3 a pressed bythe upper end of the valve spring 7 is not more than 1.20 μm isconfirmed by the endurance tests to the engine proving that the averageRa beyond 1.20 μm increases sliding frictional resistance against thevalve spring 7 to make the oxide film 14 likely to peel off.

Furthermore, as mentioned above, the spring-retaining flange 3 getsunlikely to flex, so that relative sliding of the contact surface withthe valve spring 7 involved by the flexing is prevented. Thus, the oxidefilm 14 on the outer lower surface 3 a of the spring-retaining flange 3gets more difficult to peel off.

The oxide film 14 of the outer lower surface 3 a pressed by the upperend of the valve spring 7 gets difficult to peel off. Owing to grindingeffect of peeled oxide, the contact surface of the valve spring 7 withthe spring-retaining flange 3, particularly the outer lower surface 3 aof the spring-retaining flange 3 gets more unlikely to be worn. As aresult, wear resistance on the lower surface of the spring-retainingflange 3 is improved, so that durability of the valve spring retainer 1is greatly improved.

FIG. 7 is a graph of wear of the lower surface 3 a of thespring-retaining flange 3 with respect to thickness of the oxide film 14formed on the lower surface 3 a of the spring-retaining flange 3,measured by endurance test of an engine. The wear was measured by augerspectrochemical analysis.

The engine in the endurance test is a gasoline engine of a 2000 ccdisplacement. The engine on a support operated for continuous 60 hoursat rotation speed of 6000 r.p.m. under high load and was measured.

As clearly shown in FIG. 7, the lower surface 3 a of thespring-retaining flange 3 did not wear at less than 0.02 μm or 0.00-0.02μm as thickness of the oxide film 14. Beyond 0.02 μm as the thickness,the wear gradually increased, and beyond 0.05 μm, the wear of the lowersurface 3 a proportionally increased. Even when the thickness of theoxide film 14 is zero by removing all, the lower surface of thespring-retaining flange 3 does not wear owing to the hard carburizedlayer 13.

The valve spring retainer 1 is produced with the steps in FIG. 8. Alow-carbon steel disc 15 which is 1.2-1.6 mm thick in FIG. 8 (a) ismolded with a single or a plurality of cooling or warming deep drawingsteps by a press (not shown) to a retainer original 19 comprising atubular portion 17 having a taper hole 16, and a spring-retaining flange18 at the upper end of the tubular portion 17. The original 19 is thesame as the valve spring retainer 1 in FIGS. 1-3 in shape.

Then, in a heating step 20 in FIGS. 8( c)-(e), carburizing 21, quenching22 and tempering 23 are applied to the original 19. The carburizing 21is carried out in a common gas carburizing furnace and tempering may bepreferably carried out below 300 C.

Lastly, in an oxide film removing step in FIG. 8( f), barrel finishing24 is carried out to the original 19. The oxide film formed by heatingon the lower surface pressed by the upper end of the valve spring 7 isground and removed to the thickness of 0.00-0.02 μm for predeterminedtime. Abrasives used in the barrel finishing 24 may be preferably fineparticles of size of 1.0-2.0 μm such as alumina or ceramics, therebyproviding the valve spring retainer 1 with the oxide film 14 of lessthan 0.02 μm on the lower surface of the spring-retaining flange 3. Withthe barrel finishing, center-line average Ra on the lower surface of thespring-retaining flange 3 can be made to less than 1.20 μm.

The barrel finishing is applied to the original 19 of the valve springretainer treated with heat, and the oxide film on the surface except thelower surface of the spring-retaining flange 3 is removedsimultaneously. The oxide film except the lower surface 3 a of thespring-retaining flange 3 pressed by the upper end of the valve spring 7does not affect sliding wear or does not peel off, so that it may remainwithout being removed.

Accordingly, the oxide film formed only on the lower surface of thespring-retaining flange 3 pressed by the upper end of the valve spring 7may be ground and removed to the thickness of 0.00-0.02 μm withoutbarrel finishing by another mechanical grinding means such as a grindingdisc in which a grinding wheel is used.

1. A valve spring retainer made of metal sheet in an internal combustion engine, the valve spring retainer comprising: a frusto-conical part having a taper hole; and a spring-retaining flange pressed by an upper end of a valve spring, wherein carburizing, quenching and tempering are applied to the valve spring retainer to form oxide film, the oxide film being at least partially removed at part of the spring-retaining flange pressed by the upper end of the valve spring to allow thickness of the oxide film to be 0.00-0.02 μm.
 2. The valve spring retainer of claim 1 wherein a center line average Ra of the part of the spring-retaining flange pressed by the upper end of the valve spring is not more than 1.20 μm.
 3. The valve spring retainer of claim 1 wherein the lower surface of the spring-retaining flange pressed by the upper end of the valve spring is tilted upward and outward away from the valve spring.
 4. The valve spring retainer of claim 1 wherein the outer surface of a corner between the frusto-conical part and the spring-retaining flange is formed as an arc with a radius of curvature larger than thickness of the frusto-conical part, and the inner surface of the corner facing the outer surface is formed as an arc with a radius of curvature smaller than the radius of curvature of the outer surface of the corner, so that the thickness of the corner is lager than the thickness of the frusto-conical part.
 5. A method of manufacturing a valve spring retainer made of metal sheet in an internal combustion engine, the valve spring retainer comprising a frusto-conical part having a taper hole, and a spring-retaining flange pressed by an upper end of a valve spring, the method comprising: drawing a circular metal sheet to mold an original of the valve-spring retainer; carburizing the original; quenching the original; tempering the original to form oxide film on a surface and to make the valve spring retainer; and removing the oxide film on part of the spring-retaining flange pressed by the upper end of the valve spring so that thickness of the oxide film is 0.00 to 0.02 μm.
 6. The method of claim 5 wherein the oxide film removing step includes grinding.
 7. The method of claim 6 wherein by barrel finishing of the valve spring retainer, center line average Ra at the part of the spring-retaining flange pressed by the upper end is formed to not more than 1.20 μm. 